This invention relates to receiver circuitry. More particularly, this invention relates to circuitry for receiving radio data system (“RDS”) signals.
Radio signals often include several components multiplexed together upon transmission. For example, it is relatively common for a radio signal to include both an audio signal (either stereo or monophonic) and a RDS signal, where the RDS signal contains information such as the station name, program type, music information, artist information, and traffic information. These multiplexed radio signals are often transmitted from a base station to individual users via frequency modulation (“FM”), where information is conveyed through variations of the frequency of the transmitted signal, or via amplitude modulation (“AM”), where information is conveyed through variations of the amplitude of the transmitted signal. Although the discussion herein focuses on FM signals for the purpose of clarity, it will be understood that its principles can also be applied to AM signals or any other appropriate type of signal without deviating from the spirit or scope of the invention.
When a FM signal is received, it is typically demodulated by a FM demodulator circuit and passed to both audio circuitry and RDS receiver circuitry. The audio circuitry can extract the audio portion of the signal (e.g., music or speech) and prepare it for playback through a speaker or other output device. The RDS receiver circuitry can extract the RDS portion of the signal and prepare it for processing by appropriate data processing circuitry. As an example, the data processing circuitry can display part or all of the extracted data to the user as text on a suitable user interface.
Traditionally, FM demodulator circuitry would operate in the analog domain and transmit an analog output signal to both the audio circuitry and the RDS receiver circuitry. The RDS receiver circuitry would then extract the RDS data and output it as either an analog signal or a digital signal. (If the RDS data is output as a digital signal, the RDS receiver circuitry may need to perform an analog-to-digital conversion.) However, recently it has become more common for FM demodulation circuitry to operate at least partly in the digital domain, and output a digital signal to the audio circuitry and RDS receiver circuitry. In such a scenario, it can be relatively undesirable to convert the data back into the analog domain (e.g., through the use of a digital-to-analog converter) in preparation for processing by the RDS receiver circuitry. The necessary converter would introduce unnecessary delay, consume additional area, and increase design and implementation complexity.
In view of the foregoing, it would be desirable to provide methods and apparatus that allowed RDS receiver processing in the digital domain. It would further be desirable to have digital RDS receiver circuitry that was relatively simple and consumed relatively little area.